Envelope



E. 0. VBIGKNELL. Envelope.

Patented m ay 18, 1880.

WITNESSES FHOTO-LITIIDGRAPIIER, WASHINGTON: 0.6.

IN FOR: v

WBY

I "ATTORNEYS; V

UNITED STATES.

PATENT OFFICEs EMERY O. BIOKNELL, OF BOSTON, MASSACHUSETTS.

ENVELOPE.

SPECIFICATION forming part of Letters Patent No. 227,721, dated May 18, 1880.'

Application filed J annary 30, 1880.

To all whom it may concern Be it known that I, EMERY O. BI-GKNELL, of Boston, Suffolk county, Massachusetts, have invented an Improvement in Envelopes, of which the following is a specification.

The object of the invention is to construct an envelope with means whereby attempts to open it by the application of steam or moisture will be clearly indicated, as hereinafter described.

Figures 1 and 2 exhibit a plan view of the back of envelope, the first showing the lines as applied and the second showing the change after the application of steam or water.

0n the outside of the flaps A B, and a little back of the edges, I make fine lines 0 with bronze aniline, which readily changes its color from yellowish green to a palpable brown with bright red edges on the application of water or steam. The lines are placed a short distance back of the edges and on the outside, so

as to. avoid contact with the tongue in moistening the mucilage on the inside.

I am aware that colored gum or mucilage has been used to produce a diffusion upon the application of steam or water; but, as'a sufficiency of heat and moisture may be applied to arranged on the outside of the flaps-A B and a little back of the edges, said lines being adapted to change color if the envelope is tampered with by the application of steam or moisture, as specified.

EMERY OSGOOD BIGKNELL. Witnesses:

OSCAR F. Gun, 0. 'SEDGWIQK. 

